Specimen cooling system of focused ion beam apparatus

ABSTRACT

Provided is a specimen cooling system of a focused ion beam apparatus. The specimen cooling system includes: a reaction chamber; a stage which is installed in the reaction chamber; a specimen holder which is installed over the stage and on which a specimen is placed; a heat transmission part which is attached to the specimen holder and extends from the interior of the reaction chamber to the outside so as to transmit heat, which is generated in the specimen during a process, outside the reaction chamber; and a heat sink which is connected to an end of the heat transmission part that extends from the interior of the reaction chamber to the outside and which absorbs the heat transmitted by the heat transmission part.

BACKGROUND OF THE INVENTION

This application claims the priority of Korean Patent Application No. 2003-75629, filed on Oct. 28, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

1. Field of the Invention

The present invention relates to a specimen cooling system, and more particularly, to a specimen cooling system of a focused ion beam apparatus for preventing thermal damage to a device caused by high temperature heat during the micromachining of the device using a focused ion beam.

2. Description of the Related Art

Focused ion beam (FIB) apparatuses irradiate a focused ion beam on a specific micro-part of a specimen to be micromachined so as to achieve desired micromachining. The FIB is adopted in various fields such as micromachining of devices, estimation and analysis of semiconductor processes, ion implantation processes, in-situ processes, secondary ion mass spectrometry (SIMS), and the like.

When a transmission electron microscopy (TEM) specimen is manufactured using an FIB, the FIB considerably contributes to a high-resolution analysis in a specific location of the TEM specimen. However, the FIB causes thermal damage to the TEM specimen compared to a specimen that is manufactured using a conventional ion miller. Also, it is difficult to observe in high-resolution such problems as a crystal defect, due to the thick thickness of the TEM specimen. In other words, when the TEM specimen is formed of silicon or the materials that are stable with respect to heat using the FIB, the structure of the TEM specimen is hardly affected by heat, i.e., varies only slightly. However, in a case where materials that unstable with respect to heat, for example, semiconductor materials such as high thermal conductive metal materials, InGaAs, InGaP, or the like, are micromachined using the FIB, heat is locally generated in the semiconductor materials. When the semiconductor materials are observed with a TEM, the structures of the semiconductor materials are seen to be varying due to thermal damage.

It is reported that thermal damage to a specimen manufactured with an FIB having a substantial acceleration voltage of 30 keV is about 20 nm deep.

FIG. 1 shows a conventional a temperature control apparatus. Namely, FIG. 1 is a cross-sectional view of a reactive ion etching (RIE) unit adopting a temperature control apparatus disclosed in U.S. Pat. No. 5,892,207. A temperature control apparatus 10 includes a liquid nitrogen supply device 13 which supplies liquid nitrogen into a temperature control space 12 formed in a support 11, a heating device 14 which heats the support 11, and temperature sensors 15 and 16 which detect the temperature of the support 11. When the temperature sensors 15 and 16 detect the temperature of the support 1 1 on which a wafer is mounted, a controller 18 controls the liquid nitrogen supply device 13 and the heating device 14 to cool or heat the support 11 so as to control the temperature which is set by a temperature setting device 17.

The temperature control apparatus 10 directly carries low temperature liquid nitrogen or high temperature gaseous nitrogen thereinto. Thus, the temperature control apparatus 10 must withdraw the low temperature liquid nitrogen or the high temperature gaseous nitrogen therefrom. As a result, the temperature control apparatus 10 has a complicated structure, and a vacuum in the temperature control apparatus 10 is difficult to control due to leakage of the nitrogen from the temperature control apparatus 10.

SUMMARY OF THE INVENTION

The present invention provides a specimen cooling system having a simple structure to improve high cooling efficiency so as to considerably reduce thermal damage to a target specimen during a process using an FIB.

According to an aspect of the present invention, there is provided a specimen cooling system of a focused ion beam apparatus. The specimen cooling system includes: a reaction chamber; a stage which is installed in the reaction chamber; a specimen holder which is installed over the stage and on which a specimen is placed; a heat transmission part which is attached to the specimen holder and extends from the interior of the reaction chamber to the outside so as to transmit heat, which is generated in the specimen during a process, outside the reaction chamber; and a heat sink which is connected to an end of the heat transmission part that extends from the interior of the reaction chamber to the outside and which absorbs the heat transmitted by the heat transmission part.

A trench is formed in a surface of the specimen holder to place the specimen on the specimen holder.

The specimen holder is formed of Cu, Fe, Au, or Ag.

The specimen placing part between the stage and the specimen holder

The reaction chamber includes a cooling port which is provided at a portion of the reaction chamber through which the heat transmission part penetrates.

The shape of the heat transmission part is that of a wire, a bar, or a tube.

The heat transmission part includes a portion which is formed in the shape of a wire to be attached to the specimen holder and a portion which is formed in the shape of a bar to extend from the interior of the reaction chamber to the outside through the cooling port.

The heat transmission part and the cooling port are formed of Cu, Fe, Au, or Ag.

The heat sink is a cooling vessel including a cooling medium.

The heat transmission part extends into the interior of the cooling vessel so that an end of the heat transmission part dips into the cooling medium.

The cooling medium is liquid nitrogen or liquid helium.

The heat sink is a peltier element.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a schematic cross-sectional view of a conventional temperature control apparatus for controlling the temperature of wafer;

FIG. 2 is a schematic cross-sectional view of an FIB apparatus adopting a specimen cooling system according to an embodiment of the present invention;

FIGS. 3A through 3C are cross-sectional views showing main members of the specimen cooling system of the FIB apparatus of FIG. 2;

FIG. 4A is a diagram and a photo showing a specimen manufactured using the FIB apparatus of FIG. 2;

FIG. 4B is a photo for comparing a specimen manufactured according to the present invention with a specimen manufactured according to the prior art;

FIGS. 5A through 5C are photos of the surface of a film between trench structures formed in a specimen, according to the prior art; and

FIGS. 6A through 6C are photos of the surface of a film between trench structures formed in a specimen, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of a specimen cooling system of an FIB apparatus according to the present invention will be described in detail with reference to the attached drawings. FIG. 2 is a schematic cross-sectional view of an FIB apparatus adopting a specimen cooling system, according to an embodiment of the present invention.

Referring to FIG. 2, the FIB apparatus includes a reaction chamber 21 in which a predetermined process is performed on a specimen 25, a stage 22 which is installed inside the reaction chamber 21 and over which the specimen 25 is mounted, and a specimen placing part 23. A specimen holder 24 is further provided on the specimen placing part 23 to hold the specimen 25 thereon. The specimen holder 24 is connected to a heat transmission part 26 which transmits heat of the specimen 25 to the outside during the predetermined process. The heat transmission part 26 penetrates through the reaction chamber 21 to extend to the outside and includes a cooling port 27 that is formed at a portion of the chamber 21 through which the heat transmission part 26 penetrates and that shuts the interior of the chamber 21 off from the outside. The heat transmission part 26 extends from the interior of the reaction chamber 21 to the outside and is connected to a heat sink 28. Here, the heat sink 28 absorbs heat transmitted by the heat transmission part 26 so as to cool the specimen 25.

As shown in FIG. 3C, the heat sink 28 may be a cooling vessel 30 containing a cooling medium 29 or a peltier element. When the heat sink 28 is the cooling vessel 30 containing the cooling medium 29, the heat transmission part 26 is connected to the interior of the cooling vessel 30 and dips into the cooling medium 29. The cooling vessel 30 may be a Dewar vessel. As shown in FIG. 3B, the heat transmission part 26 may be formed of flexible heat transmission wires 26 a and a fixed heat transmission bar 26 b (refer to FIG. 4) or a cooling tube.

Referring to FIG. 2, it is preferable that the specimen placing part 23 is formed by micromachining a stainless material so as not to disperse the cooling efficiency of the specimen holder 24. The specimen holder 24 serves to hold the specimen 25 thereon and transmits heat, which is locally generated in the specimen 25 during a process using an FIB, to the heat transmission part 26.

FIG. 3A is a perspective view of the specimen holder 24 used in the specimen cooling system of the FIB apparatus, according to an embodiment of the present invention. Referring to FIG. 3A, a trench structure 24 a, to which the specimen 25 is attached, is formed in the upper surface of the specimen holder 24. The specimen holder 24 may be formed to have various sizes according to an adopted process. As described above, the specimen holder 24 contacts the specimen 25 to transmit heat, which is generated in the specimen 25 during the process using the FIB, to the heat transmission part 26. Thus, it is preferable that the specimen holder 24 is formed of a material having high thermal conductivity. In otherwords, the specimen holder 24 may be formed of copper (Cu), iron (Fe), gold (Au), silver (Ag), or an alloy of Cu, Fe, Au, and Ag.

Only an adjacent portion 24 b to the trench structure 24 a contacting the specimen 25 needs to be formed of a material having high thermal conductivity so as to rapidly transmit heat, which is generated in the specimen 25 placed in the trench structure 24 a of the specimen holder 24, to the heat transmission part 26. In this case, a remaining portion 24 c of the specimen holder 24 can be formed of a material having lower thermal conductivity than the material of which the adjacent portion 24 b is formed, for example, stainless steel. The heat transmission part 26 may be attached to a side or a lower portion of the specimen holder 24. However, in a case where the heat transmission part 26 is attached to the lower portion of the specimen holder 24, the heat transmission part 26 has a relatively complicated structure.

The heat transmission part 26 is attached to a portion of the specimen holder 24 to transmit heat of the specimen holder 24 outside the reaction chamber 21. The entire heat transmission part 26 may be formed in the shape of a thin wire, tube, or bar. In view of thermal conductivity, it is preferable that the heat transmission part 26 is formed in a bar shape. However, a portion of the heat transmission part 26 may be formed in the shape of a flexible wire so that the specimen holder 24 holding the specimen 25 can move inside the reaction chamber 21 during the process. Therefore, as shown in FIG. 3B, it is preferable that the heat transmission part 26 is formed of the flexible heat transmission wires 26 a, which contact the specimen holder 24, and the fixed heat transmission bar 26 b. It is preferable that the heat transmission part 26 is formed of a material having high thermal conductivity like the specimen holder 24. In other words, the heat transmission part 26 may be formed of the same material as the specimen holder 24 or a material having high thermal conductivity. In order to improve cooling efficiency for the specimen 25, it is preferable that the heat transmission part 26 is short in length yet relatively thick.

The cooling port 27 is formed at the portion of the reaction chamber 21 through which the heat transmission part 26 penetrates to the outside. According to the present invention, the cooling port 27 may be formed of the same material as the specimen holder 24 or the heat transmission part 26 so that the heat transmission part 26 easily transmits heat from the interior of the reaction chamber 21 to the outside. The cooling port 27 may be formed of a material different from the specimen holder 24 or the heat transmission part 26 but one having high thermal conductivity. The cooling port 27 may be formed of aluminum (Al) but may be formed of Cu, Fe, Au, Ag, or the like. Preferably, a portion of the heat transmission part 26 that is formed inside the reaction chamber 21 and a portion of the heat transmission part 26 that extends outside the reaction chamber 21 form a single body, so as to prevent a gas from leaking from the interior of the reaction chamber 21 to the outside.

FIG. 3C is a sectional view of the heat sink 28 according to an embodiment of the present invention. Referring to FIG. 3C, the heat sink 28 may be the cooling vessel 30 containing the cooling medium 29. The heat transmission part 26 that goes through the cooling port 27 of the reaction chamber 21 is connected to the cooling vessel 30. The heat transmission part 26 extends into the cooling vessel 30 containing the cooling medium 29 so that an end thereof dips into the cooling medium 29. The cooling medium 29 is preferably at a low temperature and in a stable state and may be liquid nitrogen or liquid helium. In a case where the cooling vessel 30 contains low temperature liquid nitrogen, the temperature inside the cooling vessel 30 is about −179° C. Thus, the cooling vessel 30 is manufactured in consideration of the temperature of the cooling agent. The cooling vessel 30 may also be a vessel that contains general liquid nitrogen or liquid helium. The specimen cooling system of the FIB apparatus according to the present invention may use a peltier element or the cooling vessel 30 containing the cooling medium 29 as the heat sink 28.

FIG. 4A is a diagram and a photo showing a specimen manufactured adopting a process using the specimen cooling system of the FIB apparatus according to the present invention. Referring to FIG. 4A, a portion of a specimen 25 is micromachined to form a film 25 b having a thickness of about 50 to 100 nm between trench structures 25 a. The micromachining using the specimen cooling system of the FIB apparatus according to the present invention hardly causes thermal damage to the specimen 25. This will be explained in detail with reference to FIG. 4B.

FIG. 4B is a photo for comparing a specimen manufactured according to the present invention with a specimen manufactured according to the prior art. Referring to FIG. 4B, A denotes a border between trench structures 25 a and a specimen which are manufactured according to the prior art. The structure of the border A is broken and melted due to thermal damage caused during a process using an FIB. B denotes a border between trench structures 25 a and a planarized portion of a specimen which are manufactured according to the present invention. Cooling is performed during micromachining so as to hardly cause thermal damage to the border B. Thus, the border B is very clearly formed.

In the specimens manufactured according to the present invention and the prior art, the surfaces of the films 25 b between the trench structures 25 were observed separately from the specimens. This will be explained with reference to FIGS. 5A through 5C and FIGS. 6A through 6C.

FIGS. 5A through 5C are photos of the surface of a film between trench structures formed in a specimen, according to the prior art, and FIGS. 6A through 6C are photos of the surface of a film between trench structures formed in a specimen, according to the present invention. Referring to the photos of FIGS. 5A and 5B, thermal damage C, which has been caused during micromachining using the FIB, is found in the surface of the film. As shown in FIG. 5C, the film is not uniform. In contrast, as shown in FIGS. 6A through 6C, the surface of the film, which has been manufactured according to the present invention, is very clearly. In other words, when a process is performed using the specimen cooling system of the FIB apparatus according to the present invention, the film is hardly damaged by heat.

As described above, a specimen cooling system of an FIB apparatus according to the present invention can have a very simple structure to improve cooling efficiency. Thus, thermal damage to a target specimen can be considerably reduced during a process using an FIB.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 

1. A specimen cooling system of a focused ion beam apparatus, comprising: a reaction chamber; a stage which is installed in the reaction chamber; a specimen holder which is installed on the stage and on which a specimen is placed; a heat transmission part which is attached to the specimen holder and extends from the interior of the reaction chamber to the outside so as to transmit heat, which is generated in the specimen during a process, outside the reaction chamber; and a heat sink which is connected to an end of the heat transmission part that extends from the interior of the reaction chamber to the outside and which absorbs the heat transmitted by the heat transmission part.
 2. The specimen cooling system of claim 1, wherein a trench is formed in a surface of the specimen holder so that the specimen can be placed on the specimen holder.
 3. The specimen cooling system of claim 1, wherein the specimen holder is formed of at least one of Cu, Fe, Au, and Ag.
 4. The specimen cooling system of claim 1, further comprising a specimen placing part between the stage and the specimen holder.
 5. The specimen cooling system of claim 4, wherein the specimen placing part is made of a stainless material.
 6. The specimen cooling system of claim 1, wherein the reaction chamber comprises a cooling port which is provided at a portion of the reaction chamber through which the heat transmission part penetrates.
 7. The specimen cooling system of claim 6, wherein the cooling port is formed of at least one of Cu, Fe, Au, and Ag.
 8. The specimen cooling system of claim 1, wherein the heat transmission part comprises a portion which is formed in the shape of a wire and is attached to the specimen holder and a portion which is formed in the shape of a bar to extend from the interior of the reaction chamber to the outside through the cooling port.
 9. The specimen cooling system of claim 1, wherein the shape of the heat transmission part is one of a wire, a bar, and a tube.
 10. The specimen cooling system of claim 1, wherein the heat transmission part is formed of at least one of Cu, Fe, Au, and Ag.
 11. The specimen cooling system of claim 1, wherein the heat sink is a cooling vessel comprising a cooling medium.
 12. The specimen cooling system of claim 11, wherein the heat transmission part extends into the interior of the cooling vessel so that an end of the heat transmission part dips into the cooling medium.
 13. The specimen cooling system of claim 12, wherein the cooling medium is one of liquid nitrogen and liquid helium.
 14. The specimen cooling system of claim 12, wherein the cooling vessel is a Dewar vessel.
 15. The specimen cooling system of claim 1, wherein the heat sink is a peltier element. 